1. Field of the Invention
This invention relates generally to magnetic tape cassettes and more particularly to a magnetic tape cassette suitable for use for recording a digital signal, for example, a PCM (pulse code modulated) signal.
2. Description of the Prior Art
At present, a PCM recording and reproducing apparatus is proposed in which an analog signal such as an audio signal or the like is converted into a digital signal, for example, a PCM signal and then recorded on (or reproduced from) a magnetic tape. In the known PCM recording and reproducing apparatus there is known such one which uses a rotary head to afford a relatively high recording density.
In such PCM recording and reproducing apparatus having the rotary head, upon recording or reproducing, a magnetic tape is pulled out of the tape cassette, wound around the rotary drum in which the rotary head is provided, and then the recording or reproducing is carried out.
In the tape cassette accomodating therein such magnetic tape, if oil component such as fingerprints or the like and dusts adhere to the magnetic tape, a dropout is caused in the reproduced signal. So, in order to prevent the oil component such as fingerprints or the like and dusts from adhering to the magnetic tape, the magnetic tape has to be held in a closed state as tightly as possible. Further, the tape cassette must provide at its front portion a space through which a tape guide system is inserted into the tape cassette for drawing out the magnetic tape from the tape cassette upon recording or reproducing.
To this end, there is proposed such a tape cassette in which its front side at which the magnetic tape is exposed is closed by a front lid in accordance with the rotation thereof as shown in FIGS. 1 and 2. In FIGS. 1 and 2, reference numeral 1 generally designates a cassette housing and this cassette housing 1 comprises a pair of upper half 2 and lower half 3 which are fastened integral by screw bolts (not shown). Reference numeral 2a designates a transparent window plate provided on the upper surface of the upper half 2.
Reference numerals 4a and 4b respectively designate a pair of reel hubs incorporated into the cassette housing 1 and which are rotatably engaged with a pair of reel shaft insertion apertures 5a and 5b which are formed through the lower half 3 at its predetermined positions. A magnetic tape 6 is wound around the pair of reel hubs 4a and 4b.
Reference numeral 7 designates a front lid which is rotatably pivoted to the cassette housing 1 at its front surface side and near right and left side wall portions of the cassette housing 1. When this front lid 7 is rotated upwards from the front surface side of the tape cassette, the magnetic tape 6 is exposed at the front portion of the tape cassette. Reference numeral 3a designates a cut-out portion of rectangular shape formed through the bottom surface of the lower half 3 at the position near the end portion of the front portion of the tape cassette. Upon use, the tape guide system (not shown) is inserted into the cut-out portion 3a for drawing out the magnetic tape 6 from the tape cassette.
Reference numeral 8 designates a sliding member or slider of nearly U-shape which is provided such that it can be slidably moved back and forth in opposing relation to the lower surface and the right and left side wall portions of the lower half 3.
In such tape cassette, upon use, as shown in FIG. 2, the front lid 7 is rotated upwards from the front side of the tape cassette and the slider 8 is slid backward to thereby expose the magnetic tape 6 at the front portion of the tape cassette. Thereafter, the tape guide system is inserted into the cut-out portion 3a and the magnetic tape 6 is pulled out of the cassette housing 1 by this tape guide system and then loaded onto the rotary drum, whereby to carry out the predetermined recording or reproducing. After the recording or reproducing is ended and the tape cassette is set in its non-use mode, the reverse operation to the above-described operation is carried out.
In the tape cassette with the rotatable front lid 7, in order to mount the front lid 7 rotatably on the cassette housing 1, it is necessary that, as shown in FIG. 3, a bearing upper portion 10 formed on the upper half 2 at its side portion and near the front opening portion of the tape cassette and a bearing lower portion 11 formed on the lower half 3 at its side portion and near the front opening portion of the cassette are employed to constitute a bearing portion which rotatably supports therein a shaft 12 which protrudes inside of each of the side portions of the front lid 7 when the upper half 2 and the lower half 3 are fastened together.
In other words, the shaft 12 is rotatably supported in the bearing portion formed of the bearing upper portion 10 of the upper half 2 shown by a solid line and the bearing lower portion 11 shown by a one-dot chain line in FIG. 3. In this case, the shaft 12 of the front lid 7 is provided with a twist coil spring 13 which biases the portion formed through the front portion of the cassette housing 1.
When the tape cassette constructed as mentioned above is manufactured, the slider 8 must be slidably mounted on the lower half 3 and the rotary shaft 12 of the front lid 7 must be held between the bearing upper portion 10 of the upper half 2 and the bearing lower portion 11 of the lower half 3. In this case, since the front lid 7 can not temporarily be mounted on the upper half 2, there are defects that the assembling work of the tape cassette is difficult and that the number of the assembling works is inevitably increased.